Currently, data compression technologies have been widely adopted for applications such as shortening of the time required to transmit or receive data and the reduction of the size of a storage region required for storage. Accordingly, data compression apparatuses which compress data have been widely applied to, for example, a communication system that is capable of transmitting data and a data storage apparatus that stores data on a storage medium.
There are many algorithms for data compression, and compressibility changes depending on a data content and an algorithm. Accordingly, when pieces of data including the same content are compressed, compressibility typically changes in accordance with an algorithm. Assume that compressibility (%) indicates the value calculated as follows.Compressibility=(amount of data before compression/amount of data after compression)×100  (1)
The compressibility calculated in this way indicates a higher value as the compression becomes more effective, i.e., as the compression efficiency becomes higher. A compression efficiency (or compressibility) changes depending on a data content and an algorithm, and hence some conventional data compression apparatuses are provided with a plurality of kinds of data compression functions with different algorithms.
A conventional data compression apparatus provided with a plurality of data compression functions with different algorithms performs data compressions in parallel by using these data compression functions and selects an optimum piece of compressed data from pieces of compressed data obtained by the data compressions. The selection is made with reference to compressibility and a processing speed (i.e., the processing time required for the compression). As a result, such a conventional data compression apparatus selects optimum compressed data in accordance with the compressibility and the processing speed. Conventional data compression apparatuses capable of selecting optimum compressed data in this way may achieve a higher processing speed while maintaining high compressibility.
The data compression functions are each operable as one apparatus (module) so that data compressions can be performed in parallel. Accordingly, the more data compression functions are provided, the greater the power consumption of a data compression apparatus becomes. As a result, for a data compression apparatus provided with a plurality of types of data compression functions, limiting of power consumption should be considered in addition to maintenance of high compressibility and speeding up of a processing speed.    Patent document 1: Japanese Laid-open Patent Publication No. 7-210324    Patent Document 2: Japanese Laid-open Patent Publication No. 2004-13243